Field of the Invention
The present invention relates to a hybrid vehicle and a method of changing an operation mode for the same, and more particularly, to a hybrid vehicle configured for changing an operation mode related to variation in a charge of the battery in consideration of preheating of the engine, and a control method for the same.
Discussion of the Related Art
A hybrid electric vehicle (HEV) generally refers to a vehicle that uses two power sources together. The two power sources are mainly an engine and an electric motor. HEVs are recently under vigorous development since HEVs are superior to vehicles provided with an internal combustion engine in terms of fuel efficiency, power performance, and exhaust gas reduction.
The HEV is capable of operating in two modes depending on which powertrain is driven. One of the modes is an electric vehicle (EV) mode in which the HEV runs using only the electric motor, and the other mode is a hybrid electric vehicle (HEV) mode in which the electric motor and the engine are operated together to obtain power. The HEV switches between the two modes according to operation conditions.
In particular, in the case of a plug-in hybrid vehicle (PHEV), in addition to classification of the operation modes according to the powertrain described above, the operation modes may also be divided into a charge depleting (CD) mode and a charge sustaining (CS) mode based on change in the state of charge (SOC) of the battery. Generally, in the CD mode, the electric motor is driven by the electric power of the battery without the power of the engine to operate the vehicle. In the CS mode, the power of the engine is used, and wherein the battery SOC is not lowered.
In the case of a typical PHEV, the vehicle travels in the CD mode regardless of the operation conditions such as the driving load, the possibility of charging, and the distance to the destination, and then switches to the CS mode according to exhaustion of the SOC. The present case will be described with respect to FIG. 1.
FIG. 1 illustrates an example of mode switch performed in a typical PHEV.
In FIG. 1, the horizontal axis represents distance, the vertical axis of the upper graph represents the state of charge (SOC) of the battery of the PHEV, and the vertical axis of the lower graph represents driving load.
First, the lower graph of FIG. 1 depicts a route having cities, a national highway, and an expressway between the place of departure and the destination. The driving load on the route is the highest on the highway, and is higher on national highways than in cities. In running on the present route, the typical PHEV departs a place in the CD mode without considering variation in driving load, and switches to the CS mode when the SOC falls below a preset reference.
The CD mode exhibits relatively favorable efficiency in low-speed/low-load driving, and the CS mode exhibits relatively favorable efficiency in high-speed/high-load driving. Therefore, when the mode switching is performed based only on the SOC value as described above, the efficiency may be greatly lowered depending on the route because the driving load is not considered.
To address the present issue, an adaptive mode switching (adaptive CD/CS) method may be considered. The adaptive mode switching method involves automatically switching between the CD/CS modes according to the optimum efficiency using the Distance Until Charge (DUC), which is the travel distance until a next charge, the Drive To Empty (DTE), which is a travelable distance in the EV mode, an operation condition, navigation information, and the like when the vehicle travels longer than the All Electric Range (AER), which is the distance which the vehicle can travel using only the electric motor.
For example, when the adaptive mode switching method is applied, the vehicle may travel in the CS mode if the current driving load is greater than a predetermined value based on the operation condition, and travel in the CD mode if the driving load is low. Of course, if DUC≤DTE in a section where the driving load is higher than a predetermined value, the vehicle may be caused to exhaust the SOC in the DUC by operating in the CD mode. The present adaptive mode switching method will be described with respect to FIG. 2.
FIG. 2 illustrates an example of mode switch performed in a typical PHEV when an adaptive mode switching method is applied.
In FIG. 2, the meanings of the horizontal and vertical axes and the route configuration are assumed to be the same as in FIG. 1.
Referring to FIG. 2, the vehicle operates in the CD mode at startup. However, when the vehicle enters a section (the expressway in the figure) in which the driving load exceeds a preset driving load, the vehicle mode is switched to the CS mode even if the SOC is greater than or equal to a predetermined value. In a section in which DUC≤DTE, the vehicle may switch back to the CD mode, enabling efficient driving.
Once the vehicle starts traveling in the CD mode, the vehicle travels without the engine started until the mode is switched to the CS mode. Accordingly, the engine is in a cooled state at the time of switching to the CS mode. Therefore, if the power of the engine is immediately used, it is difficult to satisfy exhaust gas regulations because the temperature of the catalyst of the engine catalytic converter is low. To satisfy exhaust gas regulations, the vehicle uses the engine after performing engine warmup control to raise the temperature of the catalytic converter to the normal operating temperature. The present operation will be described with respect to FIG. 3.
FIG. 3 illustrates an example of engine warmup performed when mode switch is performed in a typical PHEV. Referring to FIG. 3, the PHEV that is configured to perform mode switch based on the SOC is configured to perform warmup control once when switching from the CD mode to the CS mode.
However, in the adaptive mode switching method, switching between modes may be repeated several times according to the operation condition, and the CS travel distance is also variable according to the driving route. Therefore, when the mode is switched from the CD mode to the CS mode, catalyst heating, namely engine warmup control, is performed to satisfy exhaust gas regulations. However, when the vehicle switches to the CD mode immediately after the short CS mode driving, fuel efficiency deteriorates due to fuel exhausted for warmup. Further, when the CS mode is re-entered after the vehicle switches from the CS mode to the CD mode, it is difficult for the vehicle to recognize the catalyst temperature. Accordingly, if the engine warmup is unconditionally performed despite the sufficiently high temperature of the catalyst when the CS mode is entered, the fuel may be wasted.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and may not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.